Specific Imaging Findings

The role of imaging in the evaluation of Alzheimer disease (AD) is to exclude other forms of dementia and identify early cases of AD which could benefit from treatment. Morphometric and metabolic measurements of the mesial temporal regions are the best imaging biomarkers for early diagnosis. In the appropriate clinical setting the diagnostic accuracy of MRI in the diagnosis of AD is approximately 87%. Typical MR findings consist of temporal and parietal cortical volume loss with prominent hippocampal atrophy. Angled coronal images perpendicular to the long axis of the hippocampus best show atrophy of the hippocampi and parahippocampal gyri with enlargement of the parahippocampal fissures.

Fluorodeoxyglucose (FDG) Positron Emission Tomography (PET) findings in the AD brain include decreased glucose uptake in the temporal and parietal lobes with sparing of the occipital and frontal lobes, while the posterior cingulate is typically affected first. FDG PET helps differentiate AD from other forms of dementia, such as vascular dementia and frontotemporal dementia, although advanced Parkinson's disease may present with a regional metabolic pattern not distinguishable from AD.

Pertinent Clinical Information

The diagnosis of AD is based on the criteria of the National Institute of Neurological and Communicative Disorders and Stroke – AD and Related Disorders Association. These standards require: insidious onset; gradual progression of memory impairment; deficits of recent memory in the early stages; impairment of orientation, judgment, problem-solving, community and home living, and personal care present later on.